Nowadays, portable electronic devices such as mobile phones and tablet computers become more and more popular. These portable electronic devices require wireless transmission of data. However, the radiation power shall be sufficiently strong to enable the data transmission of the portable electronic devices, thereby inevitably producing radiation, for example, electromagnetic radiation and/or RF radiation which is harmful to people.
A variety of radiation-proof mechanisms have been developed for controlling the radiation associated with portable electronic devices to prevent undesired exposure to people. However, these mechanisms are either expensive or less effective.
For example, the patent application US 2010/0234081 A1 has disclosed a case for redirecting away RF radiation from user side of the portable communication device, wherein a radiation-proof system in the case includes a coupling loop mounted on the back of the communication device, a signal transmitting “ladder” composed of horizontal metallic strips, and a transmitting antenna (such as a patch antenna); wherein the electromagnetic wave from an internal antenna of the portable communication device is coupled to the ladder through the coupling loop of the case, and then redirected by the patch antenna of the case in a direction away from the user, whereby reducing the amount of electromagnetic radiation directed towards the user. In the patent application, the position of the coupling loop with respect to the internal antenna is critical; and as shown in FIG. 5 of the patent application, the radiation-proof system must be placed at a distance of about 1 mm from the case of the portable communication device, which will, on one hand, make the size of the case to be relatively large, and on the other hand, it is hard for the coupling loop to be kept at an optimum position with respect to the internal antenna, whereby resulting in a less effective radiation-proof effect.
Chinese Utility Model patent ZL03249073.9 (Issue No. CN2701181Y) has disclosed a radiation-proof device for mobile phones, wherein an electromagnetic wave shielding layer is provided on an internal case and/or an external case of the mobile phone, an antenna is in electrical connection with an power amplifier feeder line and is arranged at outside of the electromagnetic wave shielding layer when the mobile phone is in an answering state, while an insulation barrier layer is provided between the antenna and the electromagnetic wave shielding layer. In the patent, the antenna is arranged at outside of the electromagnetic wave shielding layer, and the electromagnetic wave shielding layer is arranged on the case of the mobile phone, which means that the antenna must be arranged at outside of the case of the mobile phone. As the existing mobile phones on the market are basically provided with a built-in antenna, so the patent requires a modification to the structure of an existing mobile phone (particularly the antenna structure), and it could not be adapted for use as a separate protective shell mounted outside of a mobile phone.
Therefore, it is necessary for a radiation-proof material which could effectively provide the radioprotection for the user of the portable electronic devices, and particularly, could act as a separate protective case to easily mount at or detach from an electronic device.